The short answer is that absorbing a narrow band of energies is more efficient than a wide band. See: http://scienceline.ucsb.edu/getkey.php?key=4979 http://sc

The short answer is that absorbing a narrow band of energies is more efficient than a wide band. See: http://scienceline.ucsb.edu/getkey.php?key=4979 http://scienceline.ucsb.edu/getkey.php?key=4979